In thin film transistor (TFT) liquid crystal display panels, there is more electrostatic damage. Electro-static discharge (ESD) can prevent instantaneously discharged current from flowing into a pixel array of a liquid crystal display panel from damaging TFT devices in the pixels. Even if the current flows into the pixel array, the ESD can also prevent the gate electrode or the source electrode of the TFT device from generating a large voltage. Therefore, before the current flows into the pixel array, a protection circuit is designed by arranging several TFT in series or in parallel. When there is an instantaneous high current, the instantaneous high current will directly flow into the ESD to protect the pixel array.
An indium gallium zinc oxide (IGZO) TFT is referred to apply a metal oxide layer (IGZO) on an active layer of the TFT device so that migration of the channel carriers of the TFT device is significantly increased, thereby increasing response speed of the pixels.
In an IGZO 4 MASK process (IGZO TFT 4 masks process), because the channel of the TFT is larger, a source metal, a drain metal, and the IGZO layer are prepared by the same mask, and then wet-etched three times. While repeated wet etching will cause over-etching defects of the IGZO layer, and thus affect performance of the TFT device.
In summary, in current IGZO TFT fabrication process the IGZO layer will be over-etched after being etched several times, the over-etched IGZO layer will affect the performance of the TFT device and further affect response speed of the pixels of the liquid crystal display panel.